The present invention relates to video-signal recording and/or reproducing apparatus, and particularly to a helical-scan type magnetic recording and/or reproducing apparatus suitable for electrical editing of a magnetic tape without cutting and splicing the magnetic tape.
At present, two-head helical scan type video tape recorders are widely used for home video-signal recording and/or reproducing apparatus. In such video tape recorders, the record tracks for video signals are obliquely formed on the magnetic tape at a small angle with respect to the lengthwise direction of the tape. In two-head video tape recorders, each track normally contains one field of a television signal. The recent home video tape recorders generally form tracks which are each 100 .mu.m or less wide, and have no guardband between the adjacent tracks. Moreover, the magnetic tape used is generally a tape cassette which can be easily handled by any person. Therefore, it is in effect impossible to cut and splice the magnetic tape for editing the tape. Any necessary editing of the tape must be performed by continuously recording a plurality of video signals in the form of electrical signals on a single roll of magnetic tape. In addition, although the currently used tape cassette, which includes one roll of magnetic tape, is capable of about two hours of continuous recording, it is extremely rare to pick up scenes for two hours running when picture images of the scenes are recorded by the use of a video camera. That is, the picture images are divided into individual different scenes so that they are discontinuously or interruptedly picked up and recorded on the tape cassette.
In such interruption of recording (which will be referred to as discontinuous scene recording in this specification), a so-called record pause condition, for example, is effected under which only the magnetic tape is caused to stop running and the other mechanisms or parts are maintained in the recording state. When the next scene is desired to be picked up, the pause condition is released and followed by the recording condition. Thus, the discontinuous scene recording is performed by repetitions of the pause and recording states. This pause-record repetition operation is performed not only when using a video camera but also when another video apparatus is used to supply video signals which are to be edited on a single roll of magnetic tape. The pause condition is achieved usually by stopping the drive of the take-up reel and disengaging the pressure roller, which is pressing the magnetic tape against the capstan, from the capstan. When the operation mode is changed from recording to pause condition and then from pause to recording condition, it is difficult to completely stop the magnetic tape at the end of recording, and thus, the tape often slightly excessively moves further to the point at which the magnetic tape should be stopped. FIGS. 1a and 1b show record patterns on the magnetic tape when the magnetic tape is unnecessarily moved upon the repetition of record, pause and record operation modes for a discontinuous scene recording.
In FIGS. 1a and 1b, there are shown an audio-signal track 17 formed along one side edge of the magnetic tape, and a control-signal track 20 formed along the other side edge thereof. A sequence of slant elongated rectangles lying between the audio track 17 and control track 20 are alternate video signal tracks 18 and 19 of which the track 18 (a track for channel 1) is formed by one of the two video heads, and the track 19 (a track for channel 2) by the other head. For easy understanding, the track 19 for channel 2 is indicated by hatched areas. FIG. 1a shows occurence of unrecorded area between the recorded areas before and after the pause, and FIG. 1b shows an overlapped area in which the beginning of the recording after the pause is superposed upon the previously recorded area. In the case of FIG. 1a, only noise appears on the whole picture screen when the unrecorded area is reproduced, and in addition since the last portion 20a of the control signal recorded on the control track 20 just before the pause is not in phase with the initial portion 20b of the control signal after the pause, a synchronized picture can not be presented on the screen until the automatic control becomes stabilized in the tape transporting system and rotary head phase control system. In the case of FIG. 1b, although the reproduced picture does not completely disappear, the signal-to-noise ratio becomes reduced, and since the control signals are not in phase with each other at the recorded portions 20a and 20c before and after the pause similarly as in FIG. 1a, a synchronized picture can not be presented on the screen until the automatic control is stabilized, either.
To solve the problem, the following method may be considered. A part of the tape on which video signals has been recorded is rewound to a sufficient degree and is then played back to produce a control signal with which the synchronizing signal of a newly recorded signal is phase-compared, and the tape speed is controlled so that the phases of both signals coincide with each other. After the phases become coincident with each other, switching is made from the reproducing to the recording mode in which the phases of recorded signals are thus identical. In this method however, since the phase coincidence can be achieved by automatic control of the tape speed, it takes a relatively long time to reach the phase coincidence. As a result, when the next scene is picked up and recorded after the picking-up of a scene has been completed by a video camera, since a long time is required for the phase coincidence and since such delay time is not constant, various troubles occur, such as missing of a good timing at which to start recording and the missing of necessary chance at recording.